Geiger-Muller

Geiger counter Geiger-Mueller probe Geiger-Muller counters GEKKO XII Gelatin... 

Urinary excretion of radioactivity was measured in human volunteers during and after a 3.5-hour period of dermal exposure to 0.11 or 0.22 g 32P-labeled TOCP (Hodge and Sterner 1943). The specific activity of the test substance was not reported. Radioactivity in urine was measured with a Geiger-Muller counter, but the limits of detection were not reported. Maximum estimated excretion rates, 10 and 43 pg TOCP/hour for the respective dosage levels, were measured within 24 hours of initiation of exposure. Radioactivity was not detected 48 or 72 hours after dosing ceased. Cumulative radioactivity detected in urine accounted for 0.13% and 0.36% of the dermally applied radioactivity. 

DESCRIBE the operation of a Geiger-Muller (G-M) detector to include ... 

The Geiger-Muller detector is a radiation detector which operates in the G-M region. 

Gas Ionization Counters A common gas ionization counter is the Geiger-Muller counter where the electronic pulses derived from the ionization process are registered as counts. The instrument can be adjusted to detect only radiation with a desired penetrating power. 

A locally resolved detection of radioactive samples after chromatographic separation can be performed by imaging techniques which work either indirectly with Eu3+- or P-doped sensor plates and laser activated emission or directly by a micro channel array detector which works like an open Geiger-Muller counter. 

Figure 5.2 Geiger-Muller tube. The tube is filled with an ionizable gas mixture, such as neon and argon, and a voltage applied across the electrodes. Ionization of the gas by incident radiation causes a current to flow between the electrodes.

If the voltage applied to a Geiger-Muller tube is increased from zero, no response to radiation is detected despite the presence of a radioactive isotope... 

Figure 5.3 A Geiger-Muller tube for measuring the activity of liquid samples.

Lost counts correction is necessary because Geiger-Muller tubes have a dead-time in their operation. 

Use a Geiger-Muller counter (and periodically use paper discs to swipe surfaces for scintillation counting) to determine the radioisotope as well as the sites and amounts of contaminating radioactivity. 

One method of analysis of an element is based on the assumption that it can be measured using a single line, provided that line can be isolated from the rest of the spectrum. This is the basis of the method that uses equilibrated filters. The technique, used to relate the concentration of interest to the difference between two measurements, uses filters placed between the sample (or reference) and a counter of the Geiger-Muller type ... 

The emission from the radioisotopes is often insufficient to penetrate the window of a Geiger-Muller counter. Therefore, the compound whose activity is to be measured is often mixed in solution with a scintillator, called a fluor, which transforms / rays into luminescence proportional to the number of /3 particles emitted. The sample is dissolved in a solvent (toluene, xylene or dioxane, the latter being used for water-soluble compounds) that acts as a relay to transfer the energy to the scintillator. The scintillation mixture contains PPO (2,5-diphenyloxazole), which emits in the UV and POPOP, which emits in the visible and is well adapted to detection with photomultiplier tubes (Fig. 17.2). The quantum yield of emission will depend on the energy of the emitted particles. 

The sensor is a crystal of Nal(TI) that transforms the 7 photon into luminescence whose intensity is proportional to the energy of the photon (assuming that the 7 photon is entirely absorbed by the crystal). The principle is similar to that of liquid scintillators used to measure 14C. If a Ge(Li) crystal is used, it behaves like the support gas in a Geiger-Muller tube. 

Since most of the radioisotopes used in biochemical research are (3 emitters, only methods that detect and measure /3 particles will be emphasized. Two counting techniques are in current use, scintillation counting and Geiger-Muller counting... 

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